Genetics I

Question 1

What is variable expressivity?

Answer 1

Phenotype that varies among individuals with the same genotype (p.82)

Question 2

Name a classic example of a syndrome that exhibits variable expressivity.

Answer 2

Neurofibromatosis type I (NF1) (p.82)

Question 3

What is incomplete penetrance?

Answer 3

When not all individuals with a mutant genotype show the mutant phenotype (p.82)

Question 4

Name an example of a genetic mutation that exhibits incomplete penetrance.

Answer 4

BRCA1 gene mutations do not always result in breast or ovarian cancer (p.82)

Question 5

What is pleotropy?

Answer 5

When one gene contributes to multiple phenotypic effects (p.82)

Question 6

Name an example of a pleotropic condition.

Answer 6

PKU causes many seemingly unrelated symptoms ranging from mental retardation to hair/ skin changes (p.82)

Question 7

What is loss of heterozygosity?

Answer 7

When a patient inherits or develops a mutation in a tumor supressor gene, the complementary allele must be deleted/ mutated before cancer develops. This is not true of oncogenes (p.82)

Question 8

Name a condition that commonly results from loss of heterozygosity?

Answer 8

Retinoblastoma; “two hit hypothesis” (p.82)

Question 9

What is a dominant negative mutation?

Answer 9

A mutation that exerts a dominant effect. A heterozygote produces a nonfunctional altered protein that also prevents the normal gene product from functioning (p.82)

Question 10

Give an example of the process of a dominant negative mutation.

Answer 10

Mutation of a transcription factor in its allosteric site. The nonfunctioning mutatnt can still bind DNA, preventing wild-type transcription factor from binding (p.82)

Question 11

What is linkage disequilibrium?

Answer 11

The tendency of certain alleles at two linked loci to occur together more often than expected by chance. Measured in a population, not in a family and often varies across populations (p.82)

Question 12

What is mosaicism?

Answer 12

Occurs when cells in the body differ in genetic makeup due to postfertilization loss or change of genetic information during mitosis. It can refer to a germ-line mosaic condition (gondal mosaicism) where a disease is produced that is not carried by the parent’s somatic cells (p.82)

Question 13

How does a chimeric individual get his genetic makeup?

Answer 13

From 2 zygotes that subsequently fuse (p.82)

Question 14

What is locus heterogeneity? Give one example.

Answer 14

Mutations at different loci that produce the same phenotype (ex.) albinism (p.82)

Question 15

Name three conditions that exhibit locus heterogeneity and contribute to a marfanoid habitus.

Answer 15

1.) Marfan’s syndrome; 2.) MEN 2B; 3.) Homocystinuria (p.82)

Question 16

What is heteroplasmy?

Answer 16

The presence of both normal and mutated mtDNA resulting in variable expression in mitochondrial inherited disease (p.82)

Question 17

What is uniparental disomy?

Answer 17

When an offspring receives 2 copies of a chromosome from 1 parent and 0 copies from the other parent (p.83)

Question 18

What type of meiosis error is indicated by heterodisomy (heterozygous)?

Answer 18

Meiosis I error (p.83)

Question 19

What type of meiosis error is indicated by isodisomy (homozygous)?

Answer 19

Meiosis II error or postzygotic chromosomal duplication of one pair of chromosomes and loss of the other of the original pair (p. 83)

Question 20

Are conditions of uniparental disomy euploid (correct number of chromosomes) or aneuploid?

Answer 20

Euploid (p.83)

Question 21

Describe the phenotype associated with uniparental disomy.

Answer 21

Normal phenotype, however consider UPD in an individual manifesting a recessive disorder when only one parent is a carrier (p.83)

Question 22

Describe the tenents of the Hardy Weinberg Principle.

Answer 22

If a population is in Hardy Weinberg Equilibrium and p and q are the frequencies of separate alleles, then p^2 + 2pq + q^2 =1 and p + q =1 (p.83)

Question 23

What is the frequency of X-linked recessive disorders in males and females according to Hardy Weinberg logic?

Answer 23

Males = q; Females = q^2.

Question 24

Name the four assumptions of the Hardy Weinberg law.

Answer 24

1.) no mutation occurs at the locus; 2.) no selection for any of the genotypes at the locus; 3.) completely random mating; 3.) no net migration (p.83)

Question 25

What are two potential causes of genetic inactivation/ deletion?

Answer 25

1.) uniparental disomy; 2.) genetic imprinting (p.83)